The race for the Premiership is still among the top three after Merrion, Clontarf and North County all won on Bank Holiday Monday.
Niranjan Shankar took 6 for 30 as Leinster threw away a solid base to be dismissed for 219 at Anglesea Road.
A half century from Monil Patel and 45 from Gareth Delany were the highlights of a batting display that promised so much but in the end fell short of a truly challenging total.
A century stand between Dom Joyce (87) and John Anderson (73) ensured the win, and although Joe Carroll (3-43) took late wickets, the result was never in doubt, as the hosts had five wickets and 13 balls to spare.
Clontarf were pushed all the way by Phoenix at Castle Avenue.
A fourth wicket stand of 159 in 143 balls between Fletcher Coutts and New Zealand overseas player Brad Kneebone (60) propelled Phoenix to 250 for 8.
Coutts - a New Zealand club mate of Kneebone - has been Phoenix's player of the season to date - and struck 13 fours and 3 sixes in his 110.
Obus Pienaar was the pick of the attack taking 3 for 31, and it was the South African who was to be the home side hero.
He hit an unbeaten 102 from 112 balls (8 fours) sharing a fourth wicket stand of 141 with Eoghan Delany - back at the weekend from Australia - to set up the win, achieved with just two balls to spare.
The most emphatic win of the day came at Inch were 75 apiece from skipper Niall McGovern and Jonno Andrews guided County to 278 for 7.
Harry Tector (4-41) was the best of the YM attack.
The YMCA chase never materialised as they were skittled for just 105 - Oliver Gunning top scoring with 20.
County shared the wickets with two apiece for Andrew Sheridan, Malcolm Nofal, Sean Kingston and Adam Coughlan.
The Hills paid the penalty, literally, in a close contest at Sydney Parade against Pembroke.
They were hit with a 12-run penalty for slow over rate - part of 51 extras in a Pembroke total of 210 for 9.
Those runs were to come back to haunt them.
Lorcan Tucker (59) and JJ Garth (34) added 100 in 23 overs after they had been wobbling on 6 for 2.
Albert van der Merwe (3-30) brought The Hills back into the contest, but Paul Lawson (33*) added valuable late runs.
Overseas professional Daya Singh (87) looked to be winning the contest for the visitors, but three wickets apiece for New Zealand left-armer Alex Ridley and Paul Lawson saw The Hills fall 16 runs short.
With four games to go, Merrion are top, but have Clontarf and County breathing down their necks.
It's all to play for in the last month of the campaign and there are sure to be more twists and turns as the season draws to a close.
RESULTS AND LEAGUE TABLE